Metal oxide and/or organo-metal oxide compositions, including gel compositions comprising metal oxide and/or organo-metal oxides, are utilized in a variety of applications including insulation; particulate additives, including flatting agents, thickeners, fillers and reinforcing agents; adsorbents; catalyst supports; membranes; filters; radiation detectors; coatings; and dielectrics. Metal oxide and organo-metal compositions which are utilized in these applications include, but are not limited to, oxides and organo-oxides of silicon, titanium, zirconium, aluminum, iron, magnesium, molybdenum, manganese, boron, copper, zinc, vanadium, tin, nickel, tantalum, niobium, lead, yttrium or mixtures thereof. The term organo-metal oxide refers to a composition comprising a metal oxide and an organic material (i.e. a material comprising CH.sub.x functionality) which may additionally comprise other chemical groups.
Metal oxide and organo-metal oxide compositions are produced in many forms depending on their intended application. The physical forms of metal oxides and organo-metal oxide solids include powders, whiskers, platelets and fibers.
As set forth above, metal oxide and organo-metal oxide compositions also include gels comprising a metal oxide and organo-metal oxide. The term "gel" encompasses wet gels, including hydrogels and alcogels; and gels dried from the wet gels including aerogels and xerogels. The term "aerogel" was coined by S. S. Kistler in U.S. Pat. No. 2,188,007 and is generally utilized to refer to a gel which has been dried under supercritical temperature/pressure conditions. Gels, in particular aerogels, are utilized in a wide variety of applications, including thermal and acoustic insulation, catalyst supports and carriers, filters and molecular sieves, rheology control agents, reinforcing agents, thickeners and electronics, as well as the applications listed above.
Surface modified metal oxide and/or organo-metal oxide compositions have utility in many applications. For example hydrophobic metal oxide and/or organo-metal oxide compositions may be used for reinforcement and/or rheology control in elastomers and/or sealants, for example in RTV-2 (2 component, room temperature, vulcanized) type silicone sealants. Hydrophobic metal oxide and/or organo-metal oxide compositions may also be used to provide corrosion resistance and hydrophobicity in coatings. Further, hydrophobic metal oxide and/or organo-metal oxide compositions may act as a free flow agent for powdered materials to prevent caking. For example, hydrophobic metal oxide and/or organo-metal oxide compositions may be utilized in fire extinguishing powders, powdered polymers, pigments, toners, herbicides and insecticides. Still further, hydrophobic metal oxide and/or organo-metal oxide compositions may be utilized to provide rheology control and water resistance in polyester resins, in insulation coatings for moisture sensitive applications, for anti-settling purposes in aerosol paints, and for reinforcement and water repellency in dental compounds. In addition, hydrophobic metal oxide and/or organo-metal oxide compositions may be utilized as fillers, for reinforcement and rheology control rubber compositions, for example silicone rubber RTV-2 (2 component, room temperature vulcanized) compositions.
Surface modification may also be useful for other reasons. For example, surface modification may be utilized to modify the surface chemistry of the metal oxide and/or organo-metal oxide to render the metal oxide and/or organo-metal oxide more advantageous for use in particular applications. Surface modification may also be utilized to modify the dispersion characteristics of a metal oxide and/or organo-metal oxide, the adsorption characteristics of a metal oxide and/or organo-metal oxide or to modify the receptivity of the surface of the metal oxide and/or organo-metal oxide to bond to other compounds, such as coupling agents.
Metal oxide and/or organo-metal oxide compositions may comprise a fumed (pyrogenic) metal oxide, a colloidal based metal oxide, ceramic whiskers, glass fibers or a gel comprising metal oxide and/or organo-metal oxide. In the case of silica, fumed silica is generally produced by the vapor phase hydrolysis of chlorosilanes, such as silicon tetrachloride, in a hydrogen/oxygen flame. In this process, submicron sized molten spheres of silica are formed. These particles collide and fuse to form three dimensional branched, chain-like aggregates. Cooling takes place very quickly, limiting the particle growth and ensuring that the fumed metal oxide and/or organo-metal oxide is amorphous. These aggregates in turn become mechanically entangled to form agglomerates. Generally fumed silicas have B.E.T. (Brunauer Emmett Teller determined) surface areas ranging from about 50 to about 400 square meters per gram (sq.m/g). In addition, fumed silicas generally have very high purity, with total impurities, in many cases below 100 ppm.
It would be advantageous to have a process for producing surface modified metal oxide and/or organo-metal oxide compositions at ambient temperatures and/or ambient pressures.